1. Field of the Invention
The present invention relates to a method for inspecting an insulator for a spark plug used to cause an ignition in, for example, an internal combustion engine.
2. Description of the Related Art
PTL 1 discloses a method for inspecting an insulator for a spark plug. This inspection method includes a first step of applying a predetermined voltage between an electrode disposed in an axial hole of the insulator and an electrode disposed near the outer peripheral surface of the insulator. In the first step, penetration occurs at a portion of the insulator including a defect due to the applied voltage, so that the defect becomes apparent. After the first step, a second step of applying a voltage lower than the voltage applied in the first step between the two electrodes is performed. In the second step, a spark discharge that occurs at the portion including the defect that has become apparent is detected, so that the defect in the insulator is detected.